It is known, particularly in the field of iron and steel production, that it is necessary to perform a quality control on the straightness and the presence or absence of longitudinal torsions in long profiles emerging from rolling and/or drawing processes. Normally, this control is made in line on the profile advancing on a rollerway, a belt or other suitable means, by means of a plurality of detection means arranged one after the other.
One known method to perform this control provides to use a series of feeler pins separated from each other along the profile and located in contact with homologous segments of the perimeter of the profile. The feeler pins are provided to determine defects in the straightness by detecting a lack of alignment between the homologous points and possibly measuring the entity of the variation in order to signal the presence of defects beyond an allowed tolerance limit.
However, known systems are not able to guarantee totally reliable results since they cannot discriminate if a possible variation detected is due to a defect in straightness and/or to the presence of torsions along the profile, or to an unexpected displacement of the profile with respect to the nominal position of advance. In fact, if the profile is displaced even only by a little from the nominal position with respect to which the feeler pins have been located and set, this displacement can cause reading errors, leading to a mistaken evaluation of the quality of the profile.
The non-identification of profiles that are not perfectly straight can lead to serious consequences, particularly in the production of rails for tracks, linear guides or other similar products.
Detection devices that detect profiles without contact are also known, which use laser emitters suitably oriented and combined with a filming device, such as a TV camera, in order to acquire the shape of a perimeter segment of a product. By using two, three or more of these devices, arranged to make the detection on a same plane and each one oriented so as to cover, with its visual field, a specific perimeter segment which is at least partly contiguous to the segments covered by the other devices, it is possible to reconstruct the shape of profiles with extreme accuracy, even those with a complex section. An example of such devices is shown in JP-A-57-061907.
Such devices are used, for example, in the field of iron and steel production in order to control the shape and measure the section sizes of profiles emerging from rolling and/or drawing processes, and to verify that they conform to the nominal sections and/or as laid down by specifications. Such known devices are not able however to make controls or measurements of straightness or to verify the possible presence of torsions along the profiles.
DE-C-19721915 shows another example of an optical detector for steel profiles usable as rails.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain other advantages.
Purpose of the invention is to achieve a device and a method able to detect and/or measure with extreme reliability the straightness of a long product, having constant shape, and size in length, and to verify the presence or absence of longitudinal torsions along this product, in a manner that substantially cannot be influenced by variations in the position of the product to be controlled with respect to its nominal position.